In downhole drilling and completion (for example gas and oilfield exploration and production, carbon dioxide sequestration, etc.) elastomers are used in applications as diverse as packer elements, blow out preventer elements, O-rings, gaskets, and the like. The elastomers are often exposed to high temperatures and harsh chemical and mechanical subterranean environments that can degrade elastomer performance over time, reducing their reliability.
An elastomer having good chemical resistance maintains its mechanical properties, for example elasticity, extrusion resistance, and integrated structural strength, when it is contacted with various chemicals. In downhole drilling and completion applications, these chemicals include various corrosive water- and oil-based downhole fluids. Thus, in the oil and gas industry, it is more important for an elastomer to maintain its mechanical properties under “wet” rather than under “dry” conditions at given temperature and service time.
High temperature polymers that are chemically resistant under dry conditions alone are readily available. Such polymers include certain thermoplastic polyimides (TPI) and polybenzimidazoles (PBI). Chemically resistant polymers useful under wet conditions at low temperature are also readily available. Examples of these polymers include certain polyethylenes and polypropylenes. Under conditions of high temperature and corrosive fluids, fluoropolymers are often used, as they are generally considered to have the best thermal stability and chemical resistance. Examples of fluoropolymers include polytetrafluoroethylene, and certain other fluoroelastomers and perfluoroelastomers. Certain grades of fluoropolymers are claimed to have a maximum continuous service temperature of 327° C. However, even the best perfluoroelastomers can become soft at high temperature over time, losing their capability to seal gaps under high pressure. Also, fluoroelastomers or perfluoroelastomers tend to develop cracks when contacted with various downhole fluids at high temperature.
Other types of polymers such as polyetheretherketone (PEEK) have been widely used in the downhole environment as backup rings. These polymers are rigid semi-crystalline thermoplastics and can withstand high heat and exposure to caustic chemicals. However, these polymers lack elasticity and they are not desirable to be used as sealing materials. Furthermore, it is found that these polymers tend to become brittle and break apart when contacted with various corrosive downhole fluids at high temperature.
Materials having improved chemical resistance, particularly at high temperatures and under wet conditions as well as devices made of such materials that solve the above issues would be well-received in the art.